--- /dev/null
+/*
+ * Functions to sequence FLUSH and FUA writes.
+ *
+ * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
+ * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2.
+ *
+ * REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three
+ * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
+ * properties and hardware capability.
+ *
+ * If a request doesn't have data, only REQ_FLUSH makes sense, which
+ * indicates a simple flush request. If there is data, REQ_FLUSH indicates
+ * that the device cache should be flushed before the data is executed, and
+ * REQ_FUA means that the data must be on non-volatile media on request
+ * completion.
+ *
+ * If the device doesn't have writeback cache, FLUSH and FUA don't make any
+ * difference. The requests are either completed immediately if there's no
+ * data or executed as normal requests otherwise.
+ *
+ * If the device has writeback cache and supports FUA, REQ_FLUSH is
+ * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
+ *
+ * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
+ * translated to PREFLUSH and REQ_FUA to POSTFLUSH.
+ *
+ * The actual execution of flush is double buffered. Whenever a request
+ * needs to execute PRE or POSTFLUSH, it queues at
+ * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a
+ * flush is issued and the pending_idx is toggled. When the flush
+ * completes, all the requests which were pending are proceeded to the next
+ * step. This allows arbitrary merging of different types of FLUSH/FUA
+ * requests.
+ *
+ * Currently, the following conditions are used to determine when to issue
+ * flush.
+ *
+ * C1. At any given time, only one flush shall be in progress. This makes
+ * double buffering sufficient.
+ *
+ * C2. Flush is deferred if any request is executing DATA of its sequence.
+ * This avoids issuing separate POSTFLUSHes for requests which shared
+ * PREFLUSH.
+ *
+ * C3. The second condition is ignored if there is a request which has
+ * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
+ * starvation in the unlikely case where there are continuous stream of
+ * FUA (without FLUSH) requests.
+ *
+ * For devices which support FUA, it isn't clear whether C2 (and thus C3)
+ * is beneficial.
+ *
+ * Note that a sequenced FLUSH/FUA request with DATA is completed twice.
+ * Once while executing DATA and again after the whole sequence is
+ * complete. The first completion updates the contained bio but doesn't
+ * finish it so that the bio submitter is notified only after the whole
+ * sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in
+ * req_bio_endio().
+ *
+ * The above peculiarity requires that each FLUSH/FUA request has only one
+ * bio attached to it, which is guaranteed as they aren't allowed to be
+ * merged in the usual way.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/gfp.h>
+#include <linux/blk-mq.h>
+
+#include "blk.h"
+#include "blk-mq.h"
+
+/* FLUSH/FUA sequences */
+enum {
+ REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
+ REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
+ REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
+ REQ_FSEQ_DONE = (1 << 3),
+
+ REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
+ REQ_FSEQ_POSTFLUSH,
+
+ /*
+ * If flush has been pending longer than the following timeout,
+ * it's issued even if flush_data requests are still in flight.
+ */
+ FLUSH_PENDING_TIMEOUT = 5 * HZ,
+};
+
+static bool blk_kick_flush(struct request_queue *q,
+ struct blk_flush_queue *fq);
+
+static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
+{
+ unsigned int policy = 0;
+
+ if (blk_rq_sectors(rq))
+ policy |= REQ_FSEQ_DATA;
+
+ if (fflags & REQ_FLUSH) {
+ if (rq->cmd_flags & REQ_FLUSH)
+ policy |= REQ_FSEQ_PREFLUSH;
+ if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
+ policy |= REQ_FSEQ_POSTFLUSH;
+ }
+ return policy;
+}
+
+static unsigned int blk_flush_cur_seq(struct request *rq)
+{
+ return 1 << ffz(rq->flush.seq);
+}
+
+static void blk_flush_restore_request(struct request *rq)
+{
+ /*
+ * After flush data completion, @rq->bio is %NULL but we need to
+ * complete the bio again. @rq->biotail is guaranteed to equal the
+ * original @rq->bio. Restore it.
+ */
+ rq->bio = rq->biotail;
+
+ /* make @rq a normal request */
+ rq->cmd_flags &= ~REQ_FLUSH_SEQ;
+ rq->end_io = rq->flush.saved_end_io;
+}
+
+static bool blk_flush_queue_rq(struct request *rq, bool add_front)
+{
+ if (rq->q->mq_ops) {
+ struct request_queue *q = rq->q;
+
+ blk_mq_add_to_requeue_list(rq, add_front);
+ blk_mq_kick_requeue_list(q);
+ return false;
+ } else {
+ if (add_front)
+ list_add(&rq->queuelist, &rq->q->queue_head);
+ else
+ list_add_tail(&rq->queuelist, &rq->q->queue_head);
+ return true;
+ }
+}
+
+/**
+ * blk_flush_complete_seq - complete flush sequence
+ * @rq: FLUSH/FUA request being sequenced
+ * @fq: flush queue
+ * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
+ * @error: whether an error occurred
+ *
+ * @rq just completed @seq part of its flush sequence, record the
+ * completion and trigger the next step.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
+ *
+ * RETURNS:
+ * %true if requests were added to the dispatch queue, %false otherwise.
+ */
+static bool blk_flush_complete_seq(struct request *rq,
+ struct blk_flush_queue *fq,
+ unsigned int seq, int error)
+{
+ struct request_queue *q = rq->q;
+ struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
+ bool queued = false, kicked;
+
+ BUG_ON(rq->flush.seq & seq);
+ rq->flush.seq |= seq;
+
+ if (likely(!error))
+ seq = blk_flush_cur_seq(rq);
+ else
+ seq = REQ_FSEQ_DONE;
+
+ switch (seq) {
+ case REQ_FSEQ_PREFLUSH:
+ case REQ_FSEQ_POSTFLUSH:
+ /* queue for flush */
+ if (list_empty(pending))
+ fq->flush_pending_since = jiffies;
+ list_move_tail(&rq->flush.list, pending);
+ break;
+
+ case REQ_FSEQ_DATA:
+ list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
+ queued = blk_flush_queue_rq(rq, true);
+ break;
+
+ case REQ_FSEQ_DONE:
+ /*
+ * @rq was previously adjusted by blk_flush_issue() for
+ * flush sequencing and may already have gone through the
+ * flush data request completion path. Restore @rq for
+ * normal completion and end it.
+ */
+ BUG_ON(!list_empty(&rq->queuelist));
+ list_del_init(&rq->flush.list);
+ blk_flush_restore_request(rq);
+ if (q->mq_ops)
+ blk_mq_end_request(rq, error);
+ else
+ __blk_end_request_all(rq, error);
+ break;
+
+ default:
+ BUG();
+ }
+
+ kicked = blk_kick_flush(q, fq);
+ return kicked | queued;
+}
+
+static void flush_end_io(struct request *flush_rq, int error)
+{
+ struct request_queue *q = flush_rq->q;
+ struct list_head *running;
+ bool queued = false;
+ struct request *rq, *n;
+ unsigned long flags = 0;
+ struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
+
+ if (q->mq_ops) {
+ spin_lock_irqsave(&fq->mq_flush_lock, flags);
+ flush_rq->tag = -1;
+ }
+
+ running = &fq->flush_queue[fq->flush_running_idx];
+ BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
+
+ /* account completion of the flush request */
+ fq->flush_running_idx ^= 1;
+
+ if (!q->mq_ops)
+ elv_completed_request(q, flush_rq);
+
+ /* and push the waiting requests to the next stage */
+ list_for_each_entry_safe(rq, n, running, flush.list) {
+ unsigned int seq = blk_flush_cur_seq(rq);
+
+ BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
+ queued |= blk_flush_complete_seq(rq, fq, seq, error);
+ }
+
+ /*
+ * Kick the queue to avoid stall for two cases:
+ * 1. Moving a request silently to empty queue_head may stall the
+ * queue.
+ * 2. When flush request is running in non-queueable queue, the
+ * queue is hold. Restart the queue after flush request is finished
+ * to avoid stall.
+ * This function is called from request completion path and calling
+ * directly into request_fn may confuse the driver. Always use
+ * kblockd.
+ */
+ if (queued || fq->flush_queue_delayed) {
+ WARN_ON(q->mq_ops);
+ blk_run_queue_async(q);
+ }
+ fq->flush_queue_delayed = 0;
+ if (q->mq_ops)
+ spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
+}
+
+/**
+ * blk_kick_flush - consider issuing flush request
+ * @q: request_queue being kicked
+ * @fq: flush queue
+ *
+ * Flush related states of @q have changed, consider issuing flush request.
+ * Please read the comment at the top of this file for more info.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
+ *
+ * RETURNS:
+ * %true if flush was issued, %false otherwise.
+ */
+static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
+{
+ struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
+ struct request *first_rq =
+ list_first_entry(pending, struct request, flush.list);
+ struct request *flush_rq = fq->flush_rq;
+
+ /* C1 described at the top of this file */
+ if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
+ return false;
+
+ /* C2 and C3 */
+ if (!list_empty(&fq->flush_data_in_flight) &&
+ time_before(jiffies,
+ fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
+ return false;
+
+ /*
+ * Issue flush and toggle pending_idx. This makes pending_idx
+ * different from running_idx, which means flush is in flight.
+ */
+ fq->flush_pending_idx ^= 1;
+
+ blk_rq_init(q, flush_rq);
+
+ /*
+ * Borrow tag from the first request since they can't
+ * be in flight at the same time.
+ */
+ if (q->mq_ops) {
+ flush_rq->mq_ctx = first_rq->mq_ctx;
+ flush_rq->tag = first_rq->tag;
+ }
+
+ flush_rq->cmd_type = REQ_TYPE_FS;
+ flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
+ flush_rq->rq_disk = first_rq->rq_disk;
+ flush_rq->end_io = flush_end_io;
+
+ return blk_flush_queue_rq(flush_rq, false);
+}
+
+static void flush_data_end_io(struct request *rq, int error)
+{
+ struct request_queue *q = rq->q;
+ struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
+
+ /*
+ * After populating an empty queue, kick it to avoid stall. Read
+ * the comment in flush_end_io().
+ */
+ if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
+ blk_run_queue_async(q);
+}
+
+static void mq_flush_data_end_io(struct request *rq, int error)
+{
+ struct request_queue *q = rq->q;
+ struct blk_mq_hw_ctx *hctx;
+ struct blk_mq_ctx *ctx = rq->mq_ctx;
+ unsigned long flags;
+ struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
+
+ hctx = q->mq_ops->map_queue(q, ctx->cpu);
+
+ /*
+ * After populating an empty queue, kick it to avoid stall. Read
+ * the comment in flush_end_io().
+ */
+ spin_lock_irqsave(&fq->mq_flush_lock, flags);
+ if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
+ blk_mq_run_hw_queue(hctx, true);
+ spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
+}
+
+/**
+ * blk_insert_flush - insert a new FLUSH/FUA request
+ * @rq: request to insert
+ *
+ * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
+ * or __blk_mq_run_hw_queue() to dispatch request.
+ * @rq is being submitted. Analyze what needs to be done and put it on the
+ * right queue.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock) in !mq case
+ */
+void blk_insert_flush(struct request *rq)
+{
+ struct request_queue *q = rq->q;
+ unsigned int fflags = q->flush_flags; /* may change, cache */
+ unsigned int policy = blk_flush_policy(fflags, rq);
+ struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
+
+ /*
+ * @policy now records what operations need to be done. Adjust
+ * REQ_FLUSH and FUA for the driver.
+ */
+ rq->cmd_flags &= ~REQ_FLUSH;
+ if (!(fflags & REQ_FUA))
+ rq->cmd_flags &= ~REQ_FUA;
+
+ /*
+ * An empty flush handed down from a stacking driver may
+ * translate into nothing if the underlying device does not
+ * advertise a write-back cache. In this case, simply
+ * complete the request.
+ */
+ if (!policy) {
+ if (q->mq_ops)
+ blk_mq_end_request(rq, 0);
+ else
+ __blk_end_bidi_request(rq, 0, 0, 0);
+ return;
+ }
+
+ BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
+
+ /*
+ * If there's data but flush is not necessary, the request can be
+ * processed directly without going through flush machinery. Queue
+ * for normal execution.
+ */
+ if ((policy & REQ_FSEQ_DATA) &&
+ !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
+ if (q->mq_ops) {
+ blk_mq_insert_request(rq, false, false, true);
+ } else
+ list_add_tail(&rq->queuelist, &q->queue_head);
+ return;
+ }
+
+ /*
+ * @rq should go through flush machinery. Mark it part of flush
+ * sequence and submit for further processing.
+ */
+ memset(&rq->flush, 0, sizeof(rq->flush));
+ INIT_LIST_HEAD(&rq->flush.list);
+ rq->cmd_flags |= REQ_FLUSH_SEQ;
+ rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
+ if (q->mq_ops) {
+ rq->end_io = mq_flush_data_end_io;
+
+ spin_lock_irq(&fq->mq_flush_lock);
+ blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
+ spin_unlock_irq(&fq->mq_flush_lock);
+ return;
+ }
+ rq->end_io = flush_data_end_io;
+
+ blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
+}
+
+/**
+ * blkdev_issue_flush - queue a flush
+ * @bdev: blockdev to issue flush for
+ * @gfp_mask: memory allocation flags (for bio_alloc)
+ * @error_sector: error sector
+ *
+ * Description:
+ * Issue a flush for the block device in question. Caller can supply
+ * room for storing the error offset in case of a flush error, if they
+ * wish to. If WAIT flag is not passed then caller may check only what
+ * request was pushed in some internal queue for later handling.
+ */
+int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
+ sector_t *error_sector)
+{
+ struct request_queue *q;
+ struct bio *bio;
+ int ret = 0;
+
+ if (bdev->bd_disk == NULL)
+ return -ENXIO;
+
+ q = bdev_get_queue(bdev);
+ if (!q)
+ return -ENXIO;
+
+ /*
+ * some block devices may not have their queue correctly set up here
+ * (e.g. loop device without a backing file) and so issuing a flush
+ * here will panic. Ensure there is a request function before issuing
+ * the flush.
+ */
+ if (!q->make_request_fn)
+ return -ENXIO;
+
+ bio = bio_alloc(gfp_mask, 0);
+ bio->bi_bdev = bdev;
+
+ ret = submit_bio_wait(WRITE_FLUSH, bio);
+
+ /*
+ * The driver must store the error location in ->bi_sector, if
+ * it supports it. For non-stacked drivers, this should be
+ * copied from blk_rq_pos(rq).
+ */
+ if (error_sector)
+ *error_sector = bio->bi_iter.bi_sector;
+
+ bio_put(bio);
+ return ret;
+}
+EXPORT_SYMBOL(blkdev_issue_flush);
+
+struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
+ int node, int cmd_size)
+{
+ struct blk_flush_queue *fq;
+ int rq_sz = sizeof(struct request);
+
+ fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
+ if (!fq)
+ goto fail;
+
+ if (q->mq_ops) {
+ spin_lock_init(&fq->mq_flush_lock);
+ rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
+ }
+
+ fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
+ if (!fq->flush_rq)
+ goto fail_rq;
+
+ INIT_LIST_HEAD(&fq->flush_queue[0]);
+ INIT_LIST_HEAD(&fq->flush_queue[1]);
+ INIT_LIST_HEAD(&fq->flush_data_in_flight);
+
+ return fq;
+
+ fail_rq:
+ kfree(fq);
+ fail:
+ return NULL;
+}
+
+void blk_free_flush_queue(struct blk_flush_queue *fq)
+{
+ /* bio based request queue hasn't flush queue */
+ if (!fq)
+ return;
+
+ kfree(fq->flush_rq);
+ kfree(fq);
+}
Code Review / kvmfornfv.git / blobdiff